Implant for bone segment fusion

ABSTRACT

A bone screw implant is provided for immobilizing the articular surfaces of two bone segments by securing, fusing, or compression the two segments. The implant may be fabricated from a porous biocompatible metal and have a cylindrical shape and fully or partially threaded and may have variable pitch threads and a variable diameter of the shaft. The implant may include a blunt tip or a fluted self-drilling tip and a headless screwdriver socket. Large pitch cancellous threads may be in the leading-end portion of the cylinder shaft, and smaller pitch cortical threads may be at the trailing edge portion of the shaft. The implant may be fenestrated, it may have a roughened surface, and it may be coated with an osteoconductive material. The implant may be cannulated. In a specific embodiment, the implant is used for immobilizing the articular surfaces of a sacroiliac joint.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to U.S. Patent Applications62/808,454 filed Feb. 21, 2019, and 62/837,290 filed Apr. 23, 2019, thecontents of which are incorporated by reference.

FIELD OF THE INVENTION

This invention pertains to screws for securing, fusing, and/orcompressing the sacroiliac joint, vertebrae, and other bones, joints, orother bone segments.

BACKGROUND OF THE INVENTION

In orthopedics, there is frequently a need to stabilize bone segments asa result of fractures, joint dislocation, degenerative disease, or othercauses. One approach to treating any of these conditions is the use ofscrews for securing, fusing, and/or compressing two bone segmentstogether.

One method of treating a fracture across two bone fragments is driving acompression screw across the fracture site. Some compression screws mayhave a variable thread pitch along the length of the screw to aid incompressing the fracture. For fractures distal from the surface of thebone, it may be desirable to have a compression screw with no head, suchthat the screw can be inserted deeply into the bone. One example of sucha fracture is sacroiliac joint dysfunction, but many other fractures aretreated with screws to stabilize, compress and fuse bone segments.

Low back pain is a ubiquitous complaint and is second only to the commoncold for medical office visits in the US. A common etiology of low backpain is sacroiliac (SI) joint dysfunction, also referred to as“sacroiliac joint instability” or “sacroiliac joint insufficiency” dueto the lack of support of ligaments that normally stabilize the SIjoint. Common symptoms include lower back pain, buttocks pain, sciaticleg pain, groin pain, hip pain, urinary frequency, and transientparesthesia. Pain can range from dull aching to sharp and stabbing andincreases with physical activity. Symptoms also worsen with prolonged orsustained positions (i.e., sitting, standing, lying). The prevalence ofSI related pain is estimated to be in about a quarter of all patientscomplaining of low back symptoms.

The SI joint is a complex, irregular synarthrodial joint with extensivesoft tissue and ligamentous support and innervation. The joint serves asa transition from the axial spine to the pelvis. The joint has a ventralportion with articular cartilage and synovial fluid and dorsal andventral portions having a ligamentous structure. The total motion of thejoint is typically between 1°-2° rotation (nutation/counter-nutation)and 5 mm translation between sitting or standing.

Dysfunction of the SI joint in part is thought to be related topathological motion as the normal joint allows for only minimal nutationand counter-nutation and/or degeneration of the joint from variousetiologies such as trauma, repetitive injuries, childbirth, infection,and adjacent level disease (i.e., fusion of the L5-S1 segment).

Common symptoms of SI pain include pain at the sacral sulcus,sciatica-like symptoms, difficulty bearing weight to the affected side,and difficulties with static activities.

Fusion of SI joint was introduced in 1921. Smith-Petersen, M.N. (1921)“Arthrodesis of the Sacroiliac Joint. A New Method of Approach.” Journalof Bone and Joint Surgery, 67, 157-159. At the time diagnosis was madeclinically, the surgical options were limited to rather large, openprocedures. The older literature suggested more than adequate rates ofsuccess with such procedures. In the 1980s instrumented fixation becamecommon. Subsequent authors, however, were unable to reproduce similarclinical results.

Given the extensive nature and dissection of the proposed surgicalsolutions, the procedures themselves were wrought with complicationsthat included persistent pain and deep wound infections. Throughout themid-20^(th) century and into even the 1990s, enthusiasm waned for opensurgical solutions for the SI joint. Even the diagnosis itself waslargely abandoned.

Common non-surgical treatment options include therapy, support braces,medications, and guided injections. If non-surgical treatments fail toprovide adequate or sustainable relief, a minimally invasive surgery(MIS) option can be considered with the goal of stabilizing and/orfusing the SI joint.

Throughout the early 1990s and into the 21^(st) century, althoughsubstantial advancements were not made in the diagnosing of SI pain,minimally invasive surgical options with improved clinical outcomes andwith less morbidity than open procedures resulted in a reemergence ofthe diagnosis and investigational studies to better understand thedisease. This in turn, ushered in a plethora of implants designed tostabilize the SI joint in using minimally invasive techniques.

To eliminate motion across the SI joint there must be a successfulfusion between the sacrum and ilium bones that comprise the SI joint.The fusion of any two bone structures is facilitated by stability.Stability is understood as the reduction of motion across the surfacesand is enhanced by compression which creates frictional contact betweenthe surfaces.

Others have disclosed methods for the improvement of stability andstructural integrity across the joint through osseous ingrowth throughapertures/fenestrations on the body of the implant.

U.S. Pat. No. 6,053,916 discloses an implant with apertures on the bodyof the implant to allow for osseous ingrowth but does not disclose animplant having a porous structure and osteoconductive material coatingfor further bone growth enchantment.

US 2016/0310188 A also discloses a SI joint implant with fenestrationson the body of the implant.

Many patented implants are threaded. However, none have the combinationof being porous, fenestrated, surface treated, and coated withosteoconductive materials to enhance further bone growth.

SUMMARY OF THE INVENTION

In order to address the above mentioned concerns, this inventionprovides a threaded implant for the stabilization, fusion or compressionof the sacroiliac joint or other bone joints or bone segments, includingcompression and fusion of fractures. In an embodiment, the implant isfabricated from a compatible titanium or tantalum metal or alloythereof. In an embodiment, the implant is porous, fenestrated, surfacetreated, and coated with osteoconductive materials to enhance furtherbone growth. In an embodiment, an internal set of threads can support afeature such a pedicle screw, extractor, inserter, or a base for an endcap. Various thread embodiments are provided. In one embodiment, theimplant is fully threaded with large pitch cancellous threads in thedistal section, and smaller pitch cortical threads in the proximalsection. In another embodiment, a central section of the implant has nothreads. In another embodiment, the implant may have uniform threads theentire length, which can be large pitch cancellous threads or smallerpitch cortical threads.

Accordingly, in an embodiment, an implant for bone fusion or fixation isprovided. In an embodiment, the implant is a cylindrical threadedimplant fabricated from a titanium or tantalum metal or alloy with asimilar modulus of elasticity to the bone, wherein the titanium ortantalum metal or alloy is a porous material with pore sizes ranging in100 to 900 μm and a porosity of 60-65%. In an embodiment, the shaft(120) of the cylinder of the implant has a diameter between 4 mm to 14mm and length between 10 mm to 280 mm. The implant has a distal section(122) with a distal end (125), and a headless proximal section (123) anda proximal end (150) having a socket (152) for attachment to a tool thatcan rotate to screw the implant into place. The implant is threaded withlarge pitch cancellous helical threads (142) on a portion of the shaft(120), or and smaller pitch cortical helical threads (144) on a proximalportion of shaft (123), or both. In an embodiment, the implant issurface treated to have a roughened surface and is coated withhydroxyapatite (HA) or tri-calcium phosphate (TCP) or both.

In an embodiment, the implant has large pitch cancellous helical threads(142) on the shaft on a portion of the distal section, and smaller pitchcortical helical threads (144) on the shaft on a portion of the proximalsection.

In an embodiment, the implant has a channel (134) through the centerwith openings at the distal end (130) and proximal end (132) foraccepting a guidewire.

In an embodiment, the implant has one or more fenestrations (160). In anembodiment, the implant has internal threads (170) for the attachment ofan additional device such as an inserter, extractor, end cap, or modulartulip (as seen in standard pedicle screws).

In an embodiment, the distal end may be a self-drilling tip (126) withone or more teeth (127), or the distal end may be a blunt tip (129).

In an embodiment, the shaft of the implant in the section withcancellous threads may have a smaller maximum diameter than the maximaldiameter of the shaft in the section with the cortical threads, andwherein the maximum diameter of the cancellous threads are slightlysmaller than the maximum diameter of the cortical threads.

In an embodiment, threads are provided along the entire length of theimplant. In an embodiment, a central section along the longitudinal axisof the implant has no threads on the shaft. In an embodiment, theimplant has a hollow core.

In an embodiment, the fenestrations are perforations through the shaftof the implant that may be elongated on the longitudinal axis. Thefenestrations may include a channel that penetrates the implant body ina latitudinal direction. The threads may be interrupted over thefenestrations, or the threads may be continuous over the fenestrations.

In an embodiment, the implant may have uniform cortical helical threadson the entire length of the shaft. In an embodiment, an implant may haveuniform cortical helical threads on the entire length of the shaft andhave a uniform shaft diameter.

In an embodiment, the implant is used to immobilize, fuse, or compressthe articular surfaces of any bone segments or fragments, including thesacroiliac joint, the tibiotalar joint of the ankle, midfoot bones, andwrist bones.

In embodiment, a sacroiliac joint fusion implant for immobilizing thearticular surfaces of sacroiliac joint is provided with a cylindricalthreaded implant fabricated from a titanium or tantalum metal or alloywith a similar modulus of elasticity to bone, wherein the titanium ortantalum metal or alloy is a porous material with pore sizes ranging in100 to 900 μm and a porosity of 60-65%. The one or more helical threadregions between the ends may have larger pitch threads proximal to theblunt nose end of the implant and smaller pitch threads towards the backend. The implant may have a central cannulated channel extending betweenthe two ends. The implant may include screwdriver socket at the backend. The implant may be fabricated from porous titanium or tantalum oran alloy thereof, with a porosity between 60-65% with pore sizes between100 to 900 um, and the implant may have a roughened surface that isfully coated with hydroxyapatite (HA) or tri-calcium phosphate (TCP)coating.

In an embodiment, a method for fusion or immobilization of the articularsurfaces of the sacroiliac joint in relation to one another includes thesteps of placing the implant as described herein on a guidewire,drilling a suitable borehole transverse to the sacroiliac joint, andimplanting the implants transversely across the articular surfaces andthrough the sacrum and the ilium bones.

In an embodiment, a method for fusion or immobilization of the articularsurfaces of the sacroiliac joint in relation to one another includes thesteps of placing the implant as described herein on a guidewire,drilling a suitable borehole in-line to the sacroiliac joint, implantingthe implants in-line with the articular surfaces of the sacroiliacjoint.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the front (or distal end) of anembodiment of the inventive implant, showing a blunt forward end, largerpitch threads at the front and smaller pitch threads towards the back.Also shown at the tip is an opening for the cannula channel.

FIG. 2 is an elevation view of the implant of FIG. 1, showing about thefront two-thirds having larger threads and smaller shaft diameter thanthe rear one-third, which has smaller threads and a slightly largeroverall diameter.

FIG. 3 is a perspective view showing the rear (or proximal end) of theimplant of FIG. 1. The back end has an opening for the cannula channeland a socket for a screwdriver tip. A hex socket is shown, but otherembodiments are possible.

FIG. 4 is an elevation view of an alternative embodiment of theinventive implant.

FIG. 5 is a cross section of the embodiment shown in FIG. 4, cut throughthe line marked A-A.

FIG. 6 is a perspective view of the proximal end the embodiment of FIG.4.

FIG. 7 is a perspective view of the distal end of the embodiment of FIG.4.

FIG. 8 is an elevation view of the distal end of the implant of FIG. 4

FIG. 9 is an elevation view of the proximal end of the implant of FIG. 4

FIG. 10 is a perspective view of an alternative embodiment, similar toFIGS. 1-3, but having a waist section with no threads.

FIG. 11 is an elevation view of the embodiment of FIG. 4.

FIG. 12 is a perspective of an alternative embodiment of the inventiveimplant, having uniform cortical threads along the entire shaft.

FIG. 13 is an elevation view of the embodiment of FIG. 12.

FIG. 14 is a posterior view of the pelvic bone structure, showingtypical implant trajectories that secure and stabilize the sacroiliacjoint.

FIG. 15 is a sagittal view of the pelvic bone structure showing implanttrajectories.

FIG. 16 is an x-ray radiograph showing implants, sagittal view.

FIGS. 17a-g show the implant being placed in a distraction-interferencemethod. FIG. 17a shows a guide wire implanted. FIG. 17b shows theguidewire and a drill bit creating a borehole. FIGS. 17c and 17d show animplant being inserted. FIG. 17e shows a lateral view of an implant inplace. FIG. 17f is a coronal view of an installed implant. FIG. 17g is aposterior view of an installed implant.

FIGS. 18A-C show various views of trajectories that may be used for theinventive implants for stabilization, fusion, or compression of thesacroiliac joint. FIG. 18A shows a posterior view. FIG. 18B shows alateral view, with the posterior on the right. FIG. 18C shows a partialposterior view, with the bone structures rotated slightlycounterclockwise.

DETAILED DESCRIPTION

This invention provides a cylindrical, threaded, porous, coated implantfor the fusion, stabilization, or compression of two bone segments. Oneexample is fusion and stabilization of the sacroiliac (SI) joint. In anembodiment, the implant is used for arthrodesis of two bone segments inneed of fusion. The implant is fabricated from a biocompatible metal andhas the unique combination of features including a fluted or blunt tip,variable or uniform thread pitches, use of a porous material, roughenedsurface, and a coating with an osteoconductive material. The blunt tipis intended to minimize the risk of injury during implantation and tosurrounding soft tissue structures; however, a sharper tip could also befashioned that would allow for a self-tapping and/or self-drillingcapability. The inventive implants are implanted by drilling a bore holeslightly smaller than the largest diameter of the implant and screwingthe implant into position with a screwdriver.

In an embodiment, the implant is made of titanium or tantalum to matchthe modulus of elasticity of bone and is fully porous with pore sizesranging in 100 to 900 um (micron) to facilitate in-growth and have aporosity of 60-65% to mimic cancellous bone, which would allow forbetter osseointegration. In addition, the implant would be either asolid porous implant and/or slotted/fenestrated to allow for graftplacement.

In an embodiment the implant has a diameter of 4 mm to 14 mm and lengthfrom 10 mm to 280 mm. In use, a kit may be provided for use in theoperating theater with a variety of sizes.

In an embodiment, all surfaces of the implant are roughened with a macrosurface roughness which may be accomplished with a technique such asgrit blasting, acid etching, or plasma spray coating (also calledthermal spray coating).

In an embodiment, all surfaces of the implant are coated withhydroxyapatite (HA) and/or tricalcium phosphate (TCP), with a coatingthickness of approximately 35 μm (range 15-50 μm). Both HA and TCP areosteoconductive materials that encourage bone growth.

In an embodiment of the present invention, the implant is cannulated toallow for insertion via a guidewire.

The implant is either fully threaded as shown on FIGS. 1-9 and 12-13 tostabilize the joint, or partially threaded as shown on FIGS. 10-11 tostabilize and compress the joint. The threads may vary in size andpitch. In an embodiment, the implant may have larger pitch cancellousthreads in a distal section, and small pitch cortical threads in aproximal section. This configuration will compress two bone fragments,drawing them together for arthrodesis of the interface between two bonesegments. In an embodiment when used for compression of the SI joint,the portion of the implant inserted into the sacrum may have large pitchcancellous threads, while the portion of the screw that secures to theilium would have smaller pitch cortical threads. In an embodiment, theimplant may have uniform threads (FIGS. 12-13), which stabilizes thejoint.

FIG. 1 is a perspective view of an embodiment of the inventive implant100, showing the body 120 of the implant, having a blunt nose 129 (thedistal end), which is the leading end of the implant and a back end 150(the proximal end).

As used herein, the “distal” and “proximal” descriptors are in relationto the surgeon implanting the device. Thus, the nose (or tip) end (125)is distal to the surgeon during implantation. This distal end is alsoreferred to as a “tip,” the “front,” “nose,” or “leading end.” The backend 150 with the screwdriver socket (152) is closer to the surgeon andis therefore the proximal end. The inventive implants have alongitudinal axis running from the nose end 125 to the back end 150.This is illustrated as line A-A in FIG. 4. A latitudinal cross sectioncan be made at any point perpendicular to the longitudinal axis.

As shown in FIGS. 1-3, implant embodiment 100 has a blunt tip 129 at thenose 125. Other embodiments of nose 125 possible, for example embodiment108 as shown in FIGS. 4-9. The blunt tip nose 129 may be useful tominimize tissue damage during insertion of the implant.

In the embodiment 100 illustrated in FIGS. 1-3, the helical threads 140on the distal end of the implant are large pitch cancellous threads 142.In an embodiment, these threads may have a pitch of 2.75 mm and a threadheight H of 2.00 mm. As shown in FIGS. 1-3, the forward 75%(approximately) of the implant employs cancellous threads, and theproximal remainder of the implant has smaller pitch cortical threads.

In the embodiment illustrated in FIGS. 1-3, the threads 140 on theproximal end of the implant are smaller pitch cortical threads 144. Asillustrated, the cortical threads have a pitch of 1.75 mm and a threadheight H of 1.50 mm.

In the embodiment illustrated in FIGS. 1-3, the implant body 120 doesnot have a uniform diameter. This is a function of the requirement thatthe cortical threads have a slightly larger overall diameter (Dmaj) thanthe cancellous threads. This is necessary because during implantation,the cortical threads follow the cancellous threads into the bore holedrilled for the implant. If the rear thread were not slightly larger,the implant would not nest snugly in its final position. Since thecancellous threads in the forward two-thirds of the illustrated implantare larger threads, the body of the implant must be reduced in diameterto accommodate the larger threads in the cancellous-threaded section,and the requisite smaller Dmaj than the cortical-threaded section. Atransition zone 124 is present between the two sections.

Thus, a representative set of dimensions for the two zones of theimplant (FIGS. 1-3 and 10-11) may be:

Cancellous threads, Dmaj=10.5 mm, Dmin=8.5 mm, P=2.75 mm

Cortical threads, Dmaj=11.0 mm, Dmin=9.5 mm, P=1.75 mm

Where Dmaj is the major diameter, which is the maximum diameter of thethread. Dmin is the minor diameter, which in effect is the diameter ofthe body of the shaft in this embodiment. P is the thread pitch. TypicalISO 261 or Unified Thread Standard (UTS) dimensions may be used for thescrew thread dimensions.

In the embodiment of FIGS. 4-7, the proximal section with corticalthreads has an increased diameter with a horn-shaped profile with amaximal diameter at the proximal end 150.

Thus, as illustrated in FIGS. 1-3, the maximal diameter(Dmaj)(cancellous) of the cancellous threads is 0.5 mm smaller than themaximal diameter (Dmaj)(cortical) of the cortical threads. In anembodiment, this diameter differential may vary from about 0.1 mm to 1.0mm.

The embodiment shown in FIGS. 1-3 illustrates a typical embodiment ofthis invention. The implant 100 comprises a cylindrical body, circularin latitudinal cross section, that is about 10-280 mm long. The lengthof the implant in these illustrations is 60 mm. A blunt tip 125 is shownon the distal end for minimizing damage to tissues during the insertionprocedure. A cannula channel 134 may be provided along the longitudinalaxis of the implant, for placement using a guide wire. The distalopening of the cannula channel is 130. The forward (distal)approximately 75% of the length of the implant, 122, is threaded withcancellous threads 142. The proximal section of the shaft, 123, isthreaded with cortical threads. As discussed above, the cancelloussection 122 has a smaller diameter than cortical section 123.

FIG. 3 is a perspective view showing the distal (back) end 150 of theimplant 100 of FIG. 1. The structure of the back end is typical for allimplants of this invention. The proximal end of the implant is headlessand includes a screwdriver socket 152, depicted in FIG. 3 as a hexsocket. This socket can be in any of several shapes for accepting ascrewdriver, for example, a Phillips screw socket, “Torx” socket, or ahex socket. Also depicted in FIG. 3 is orifice 132, which is theproximal outlet for the cannula channel along the centerline of theimplant. The overall structure of the proximal end of the inventiveimplants (150, 152, 132) may the same across other embodiments, forexample those depicted in FIGS. 4, 10, and 12.

An alternative embodiment of a fully threaded implant 108 is shown inFIGS. 4-9. This embodiment includes a taper 128 in shaft 120 towards tip126. Tip 126 is fluted and has teeth 127. This fluted tip can also betermed a “self-tapping” or “self-drilling” screw tip. FIG. 4 is anelevation view of this implant. Several fenestrations 160 are shown, forbone through growth. The fenestrations are shown as ellipticalperforations that pass completely through the body 120 of the implant.The proximal end of implant 108 is has cortical threads and is flared(154) outward slightly, with a horn-like shape. A perspective view ofthe proximal end of 108 is shown in FIG. 6. A perspective view showingthe distal end is in FIG. 7.

A cross sectional view of implant 108 is shown in FIG. 5, showing a viewthrough line A-A is FIG. 4. Body 120 is seen with taper 128 at thedistal end and flare 154 at the proximal end. Central channel 134 isshown, along with channel taper sections 133. The cross section bisectsone of fenestrations 160.

FIG. 5 also shows internal threads 170. These threads are a potentialfeature of any embodiment of this invention. Threads 170 are femalethreads in central channel 134 at the proximal end of the implant,adjacent to the screwdriver socket 152. These threads can be used for avariety of purposes. For example, a short shaft screw (i.e., having malethreads) with a tulip as seen with standard pedicle screws can beinserted for anchoring a rod system. Other examples that can be screwedinto threads 170 include an inserter, an extractor, or a plug or capthat may extend to cover end 150. The cap can be used to minimize lossof bone grafts. For example, channel 130 may be packed with bonefragments from an autograft or allograft, which may facilitate bonegrowth. A cap over 150 will keep the bone fragments in place.

End views of the implant 108 are shown in FIGS. 8 and 9. FIG. 8 is anelevation view of the distal tip, showing flutes (teeth) 127, centralchannel 134, taper 133, and threads 140. FIG. 9 is an elevation view ofthe proximal end (150) of the implant, shown screwdriver socket 152 (atorx socket is shown), channel 134 and opening 132, and threads 170.

The embodiment 102 in FIGS. 10-11 is similar to FIGS. 1-3, except thatthis embodiment has a waist section 146 with no threads. Thus, there isa section of cancellous threads 142 on a distal portion of the body, anda section of cortical threads 144 on the proximal section of the body,and no threads in the center section. This type of implant may be usedfor compression of joints, including the SI joint.

The embodiment 106 of FIGS. 12-13 has uniform thread dimensions and auniform shaft diameter. In this embodiment as shown, the implant hascortical thread dimensions (144) throughout, but an alternativeembodiment can have larger diameter cancellous threads throughout. FIGS.10-13 are illustrated with blunt tip 125/129, but these embodiments arealso possible with fluted tip 126/127.

In an embodiment, the implants 100, 102, 106, and 108 may haveperforations 160 for bone through-growth (also termed herein“fenestrations”). In an embodiment, the threads 140, 142, or 144 areinterrupted over the fenestrations. In an alternative embodiment, thethreads are continuous over the fenestrations. In an embodiment, thefenestrations 160 penetrate completely through the body of the implantlatitudinally. In an embodiment, the fenestrations are slots orapertures, elongated in the longitudinal direction of the implant.

In a further embodiment, the implant may have a hollow core. In anembodiment, the implant may have a solid core, that is, without acentral channel 134.

In an embodiment, the entire implant is fabricated from medicallycompatible tantalum, titanium, tantalum alloy, or titanium alloy. Forexample, an appropriate titanium alloy may be titanium 6Al4V and 6Al4VELI (ASTM Standard F1472, https://www.astm.org/Standards/F1472.htm (seealso https://en.wikipedia.org/wiki/Ti-6Al-4V)), which are alloys madewith about 6% aluminum and 4% vanadium. An appropriate tantalum alloymay be tantalum alloyed with 2.5% to 10% tungsten, or 40% niobium. Thesematerials are known to have good biocompatibility and match the modulusof elasticity of bone. In an embodiment, the implant may be manufacturedfrom a titanium alloy in accordance with ASTM F136, or where exteriorsurfaces are coated with medical-grade commercially pure titanium (CPTi) per ASTM F1580.

In an embodiment, the implant may be fabricated from a titanium ortantalum material as described above that is also porous, which is knownto enhance bone in-growth, for example with pore sizes ranging in 100 to900 μm and with a porosity of 60-65% to mimic cancellous bone. Porosityis a measure of the void (i.e. “empty”) spaces in a material and is afraction of the volume of voids expressed as a percentage. Pore sizes ofabout 600 μm have been recommended as optimal for bone ingrowth (N.Taniguchi, et al., “Effect of pore size on bone ingrowth into poroustitanium implants fabricated by additive manufacturing: An in vivoexperiment,” Mater Sci Eng C Mater Biol Appl. 2016 February; 59:690-701.doi: 10.1016/j.msec.2015.10.069. Epub 2015 Oct. 28). In an embodiment,the pore sizes may be 300-400 μm. Li, G., Wang, L., Pan, W. et al. Invitro and in vivo study of additive manufactured porous Ti6Al4Vscaffolds for repairing bone defects. Sci Rep 6, 34072 (2016).https://doi.org/10.1038/srep34072. In an embodiment, any pore sizerecitation herein may have a tolerance of ±50 μm. In an embodiment, thepores may have uniform shapes, or have random shapes.

The combination of fenestrations, surface roughness, HA or TCP coating,and porosity will facilitate bone in-growth which is desirable forfusion of the implants to surrounding bone.

In use, the implants are preferably implanted using minimally invasivemethods. In an exemplary method, there are four principal steps of thesurgical procedure. These are: minimally invasive lateral access viadilators and image guidance, joint preparation via drills or currettes,bone graft placement, and implant delivery. Various implant trajectoriesare possible.

In one aspect, a method is provided for stabilizing the SI joint byinserting a single or multiple implants from a lateral to medialdirection, transverse to the SI joint. FIG. 14 is a posterior view ofthe pelvic bone structure, showing transverse implant placements 230that secure and stabilize the sacroiliac joint 220 with the distalportion of the implant inserted in the sacrum 210 and the proximalportion of the implant embedded in the ilium 200.

FIG. 15 is a sagittal view of the pelvic bone structure showing implanttrajectories and the movement of the sacrum 210 with respect to ilium200 is shown with arrows, with the implants 230 traversing the sacrum210 and ilium 220. The method includes dissecting through the glutealmuscles, drilling/advancing the implant through the ilium, traversingthe SI joint, entering the sacrum and stopping just lateral to thesacral foramen and/or neural elements.

FIG. 16 is an x-ray radiograph sagittal view showing various implants,including sacroiliac joint implants designated by an arrow in thetransverse trajectory.

In another embodiment, the method for stabilizing the SI includesinserting the implant through an in-line trajectory, namely in adistraction arthrodesis manner in which the implant would enter at theposterior/superior aspect of the joint and advance caudally and in-linewith the SI joint, as shown on FIGS. 17 and 18.

FIG. 17 is a series of x-ray radiographs for a similar implant, showingthe implant being placed using a distraction-interference method. FIG.17a shows a guide wire implanted. FIG. 17b shows the guidewire and adrill bit creating a bore hole along the guide wire. FIGS. 17c and 17dshow the implant being inserted. FIG. 17e shows a lateral view of animplant in place. FIG. 17f is a coronal view of the installed implant.FIG. 17g is a posterior view of the installed implant.

FIG. 18 shows various views of a trajectory 240 that may be used forthis implant, in a trajectory where the implant is positioned within thesacroiliac joint, rather than across the joint. FIGS. 12A-C showdifferent views of the same trajectory 240 that is made from theposterior to the anterior direction at an angle pointing downward, i.e.,the caudal direction. FIG. 18A shows a posterior view with the implantinserted into the joint across the center plane of the patient. FIG. 18Bshows a lateral view of the same trajectory, with the posterior on theright. FIG. 18C shows a partial posterior view, with the bone structuresrotated slightly counterclockwise.

In an exemplary procedure, a 1.5-2 cm incision is made, and a dilatorand guide pin are used to access the ilium and SI joint underfluoroscopic guidance. A cannulated drill is then advanced over theguide pin to create an osseous tunnel through the ilium and/or sacrum.The drillings are collected for use in the bone graft, avoiding the needfor direct ICBG harvest. The joint is prepared by removing cartilage anddecorticating the joint area surrounding the tunnel, while irrigationand suction are used to extract joint tissue. Approximately 5 cc bonegraft, including autologous bone from the drillings, is then packed intothe implant.

Fixation is then achieved with at least one cannulated implant, and oneor more additional implants to ensure rotational stability. Finalfluoroscopic images are obtained to confirm correct placement, and thedeep tissues and skin incision may be infiltrated with bupivacaine andepinephrine for postoperative pain control. Fusion status is typicallyassessed with CT 12 months after the procedure if indicated.

Drawings Legend 100 Implant with continuous threads cancellous andcortical 102 Implant with no threads in the center section 106 Implantwith cortical threads only, uniform shaft diameter 108 Implant withfluted tip, flared proximal section 120 Implant body (shaft) 122 Implantbody (shaft)- cancellous (distal) section 123 Implant body (shaft) -cortical (proximal) section 124 Body transition section 125 Nose (tip)(distal end) of implant 126 Self- drilling tip 127 Teeth (flutes) ondistal tip 128 Taper on shaft at distal end 129 Blunt tip 130 Centralchannel opening at the distal end 132 Central channel opening at theproximal end 133 Internal taper in central channel 134 Central channel140 Threads 142 Cancellous Threads at the distal end 144 CorticalThreads at the proximal end. 146 Central section with no threads 150Back (proximal) end 152 Screwdriver socket 154 Flare in proximal section160 Perforation for bone in-growth 170 Internal threads 200 Ilium 210Sacrum 220 Sacroiliac joint 230 Inventive implants in position 240Implant trajectory

1. An implant for bone fusion or fixation, comprising a. A cylindricalthreaded implant fabricated from a titanium or tantalum metal or alloywith a similar modulus of elasticity to the bone, wherein the titaniumor tantalum metal or alloy is a porous material with pore sizes rangingin 100 to 900 μm and a porosity of 60-65%; b. wherein the shaft (120) ofthe cylinder of the implant has a diameter between 4 mm to 14 mm andlength between 10 mm to 280 mm; c. wherein the implant has a distalsection (122) with a distal end (125); d. wherein the implant has aheadless proximal section (123) and a proximal end (150) having a socket(152) for attachment to a tool that can rotate to screw the implant intoplace; e. wherein the implant is threaded with large pitch cancelloushelical threads (142) on a portion of the shaft (120), or smaller pitchcortical helical threads (144) on a portion of shaft (123), or whereinthe implant has uniform threads (FIG. 12, 142); f. wherein the implanthas at least one fenestration (160) penetrating through the body of theimplant latitudinally, where the fenestration facilitates bonethrough-growth; g. wherein the implant is surface treated to have aroughened surface; and h. wherein the implant is coated withhydroxyapatite (HA) or tri-calcium phosphate (TCP) or both.
 2. Theimplant according to claim 1, further comprising threads along theentire length of the implant.
 3. The implant according to claim 1,further comprising a central section having no threads on the shaft. 4.The implant according to claim 1, wherein the implant has large pitchcancellous helical threads (142) on the shaft on a portion of the distalsection, and smaller pitch cortical helical threads (144) on the shafton a portion of the proximal section.
 5. The implant according to claim1, wherein the distal section has large pitch cancellous threads, theproximal section has smaller pitch cortical threads, and the proximalsection has a flare (154).
 6. The implant according to claim 1, whereinthe shaft in the section with cancellous threads (122) has a smallerdiameter than the diameter of the shaft in the section with the corticalthreads (123), and wherein the maximum diameter of the cancellousthreads are slightly smaller than the maximum diameter of the corticalthreads.
 7. The implant according to claim 1, wherein the implant has achannel (134) through the longitudinal axis with openings at the distalend (130) and proximal end (132) for accepting a guidewire. 8.(canceled)
 9. (canceled)
 10. The implant according to claim 1, whereinthe porous titanium or tantalum metal or alloy has pore sizes of 300 to400 μm.
 11. The implant according to claim 1, wherein the poroustitanium or tantalum metal or alloy has a pore size of 600 μm.
 12. Theimplant according to claim 1, wherein the implant has internal threads(170) for the attachment of an additional device.
 13. The implantaccording to claim 1, wherein the distal end comprises a self-drillingtip (126) with one or more teeth (127).
 14. The implant according toclaim 1, wherein the distal end comprises a blunt tip (129). 15.(canceled)
 16. The implant according to claim 1, wherein the implant isused to immobilize the articular surfaces of a sacroiliac joint.
 17. Afusion or fixation implant for immobilizing the articular surfaces of ajoint or segment of bone or fracture comprising: a. A cylindricalthreaded implant fabricated from a titanium or tantalum metal or alloywith a similar modulus of elasticity to the bone, wherein the titaniumor tantalum metal or alloy is a porous material with pore sizes rangingin 100 to 900 μm and a porosity of 60-65%; b. wherein the shaft of thecylinder of the implant has a diameter between 4 mm to 14 mm and lengthbetween 10 mm to 280 mm; c. wherein the implant has a distal sectionwith a fluted distal end (126, 127); d. wherein the implant has a flaredheadless proximal section (123) and a proximal end (152) having a socket(152) for attachment to a tool that can rotate to screw the implant intoplace; e. wherein the implant is fully threaded with large pitchcancellous helical threads (142) on the shaft on a portion of the distalsection, and smaller pitch cortical helical threads (144) on the shafton a portion of the proximal section; f. wherein the implant has acentral channel (134) longitudinally spanning the entire length; g.wherein a set of secondary female threads (170) is in the centralchannel adjacent to the socket in the proximal end; h. wherein theimplant has one or more fenestrations (160); i. wherein the implant issurface treated to have a roughened surface; and j. wherein the implantis coated with hydroxyapatite (HA) or tri-calcium phosphate (TCP) orboth.
 18. A fusion or fixation implant for immobilizing the articularsurfaces of a joint or segment of bone or fracture comprising: a. Acylindrical threaded implant fabricated from a titanium or tantalummetal or alloy with a similar modulus of elasticity to bone, wherein thetitanium or tantalum metal or alloy is a porous material with pore sizesranging in 100 to 900 μm and a porosity of 60-65%; b. wherein the shaftof the cylinder of the implant has a diameter between 4 mm to 14 mm andlength between 10 mm to 280 mm; c. wherein the implant has a distalsection with a distal end with a rounded tip; d. wherein the implant hasa headless proximal section and a proximal end having a socket forattachment to a tool that can rotate to screw the implant into place; e.wherein the implant has uniform cortical helical threads on the entirelength of the shaft; f. wherein the implant has a channel through thecenter with openings at the distal end and proximal end for accepting aguidewire; g. wherein the implant has one or more fenestrations; h.wherein the implant is surface treated to have a roughened surface; andi. wherein the implant is coated with hydroxyapatite (HA) or tri-calciumphosphate (TCP) or both.
 19. (canceled)
 20. (canceled)
 21. The implantof claim 12, wherein a feature with male threads is screwed into theinternal female threads (170), wherein the feature is selected from apedicle screw, an extractor, an inserter, or a cap for the proximal end.22. The implant of claim 17, wherein a feature with male threads isscrewed into the internal female threads (170), wherein the feature isselected from a pedicle screw, an extractor, an inserter, or a cap forthe proximal end.